Global analysis of ocean phytoplankton nutrient limitation reveals high prevalence of co-limitation

Nutrient availability limits phytoplankton growth throughout much of the global ocean. Here we synthesize available experimental data to identify three dominant nutrient limitation regimes: nitrogen is limiting in the stratified subtropical gyres and in the summertime Arctic Ocean, iron is most commonly limiting in upwelling regions, and both nutrients are frequently co-limiting in regions in between the nitrogen and iron limited systems. Manganese can be co-limiting with iron in parts of the Southern Ocean, whilst phosphate and cobalt can be co-/serially limiting in some settings. Overall, an analysis of experimental responses showed that phytoplankton net growth can be significantly enhanced through increasing the number of different nutrients supplied, regardless of latitude, temperature, or trophic status, implying surface seawaters are often approaching nutrient co-limitation. Assessments of nutrient deficiency based on seawater nutrient concentrations and nutrient stress diagnosed via molecular biomarkers showed good agreement with experimentally-assessed nutrient limitation, validating conceptual and theoretical links between nutrient stoichiometry and microbial ecophysiology.

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Policy information about availability of of data All manuscripts must include a data availability statement This statement should provide the following information, where applicable: -Accession codes, unique identifiers, or or web links for publicly available datasets -A description of of any restrictions on on data availability -For clinical datasets or or third party data, please ensure that the statement adheres to to our policy The results of oceanic nutrient enrichment bioassay experiments were collated from the literature alongside associated meta data (where available). This dataset was then analyzed to globally assess spatial patterns of oceanic nutrient limitation, quantitatively evaluate the response of phytoplankton to nutrient supply, and assess potential drivers. Only studies where nutrient enrichments were conducted with at least triplicate independent biological replicates were included in the dataset, apart from a small number of mesoscale (km scale) oceanic iron enrichment experiments that were also included. The assembled dataset included experiments conducted with both factorial and non-factorial sets of nutrient additions.
Experimental data was synthesized from the literature. Only studies where nutrient enrichments were conducted with at least triplicate replication were included in the dataset, apart from a small number of mesoscale (km scale) oceanic iron enrichment experiments that were also included. The complete dataset, with accompanying references for each individual experimental treatment, is provided in both Supplementary Data 1 and uploaded to Zenodo (see 'Data availability' statement).
All experiments found in the literature conforming to the requirements described above were included.
Data were either extracted from the manuscript itself, obtained directly from the authors of the relevant study, a web-based data extractor tool was used to obtain data from publication figures (https://automeris.io/WebPlotDigitizer), or these data were not included in the dataset. Data collation was conducted by T. Browning, M. Moore, and G. Vickery.
Data collation (that is, assembly of the bioassay experiment dataset) was conducted between 2019 and 2021 with irregular frequency (determined by time available for this project and as new studies became available in the literature).
No data that fit the requirements outlined below (for treatment replication) were excluded from the analysis.
Only experiments in the literature using at least triplicate replication were included in the dataset, apart from a small number of mesoscale (km scale) oceanic iron enrichment experiments that were also included. Attempts at replication by the authors of these studies were assumed successful in all cases.
No randomization was used in the data analysis.
The investigators were not blinded during dataset assembly (that is, extraction of the bioassay data from the various publications), however, further data analysis with the assembled dataset was conducted without information about either the authors or manuscript titles of the individual source studies.